Method for purifying sulfuric acid

Abstract

This provides an inexpensive method for purifying sulfuric acid. [Solution] The present invention provides a method for purifying sulfuric acid, comprising an extraction step of extracting iron from sulfuric acid using an acidic organophosphorus compound, wherein the acidic organic extractant comprises at least one selected from the group consisting of 2-ethylhexyl 2-ethylhexyl phosphonate and bis(2,4,4-trimethylpentyl)dithiophosphinic acid. This method for purifying sulfuric acid may also include a back-extraction step of back-extracting the extract obtained through this extraction step to obtain a back-extract containing iron, a dilution step of diluting concentrated sulfuric acid with water, and an oxidation step of oxidizing sulfuric acid with an oxidizing agent.

Description

Technical Field

[0001] The present invention relates to a method for purifying sulfuric acid.

Background Art

[0002] Impurities such as iron are contained in industrial sulfuric acid. Therefore, methods for purifying industrial sulfuric acid have been studied. Patent Document 1 discloses a method for purifying sulfuric acid in which sulfuric acid containing a metal such as iron is purified by using a monodisperse chelating exchanger.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The monodisperse chelating exchanger is very expensive, and the cost of the purification method was high.

[0005] The problem to be solved by the present invention is to provide a method for purifying sulfuric acid at a low cost.

Means for Solving the Problems

[0006] In view of the above problems, the present inventors have conducted extensive studies and found that the cost of a method for purifying sulfuric acid including an extraction step of extracting iron from sulfuric acid using a specific acidic organic phosphorus compound is low. The present invention has been completed based on these findings.

[0007] The present invention is a method for purifying sulfuric acid, comprising an extraction step of extracting iron from sulfuric acid using an acidic organic phosphorus compound, and a back-extraction step of back-extracting the extract obtained through the extraction step with an acid to obtain a back-extract containing iron, wherein the acidic organic Phosphorus compoundsThis comprises at least one selected from the group consisting of 2-ethylhexyl 2-ethylhexyl phosphonate and bis(2,4,4-trimethylpentyl)dithiophosphinic acid, and the acid contains oxalic acid. The method for purifying sulfuric acid preferably further includes a dilution step in which concentrated sulfuric acid is diluted with water. The method for purifying sulfuric acid preferably further includes an oxidation step in which the iron contained in the sulfuric acid is oxidized with an oxidizing agent. [Effects of the Invention]

[0008] The present invention provides a method for purifying sulfuric acid at a low cost. [Brief explanation of the drawing]

[0009] [Figure 1] An explanatory diagram showing the configuration of one embodiment of the sulfuric acid purification method of the present invention. [Modes for carrying out the invention]

[0010] The present invention will be described in more detail.

[0011] The present invention provides a method for purifying sulfuric acid, comprising an extraction step (STEP 2 in Figure 1) in which iron is extracted from sulfuric acid 1 using an acidic organophosphorus compound 4. The acidic organophosphorus compound 4 comprises at least one selected from the group consisting of 2-ethylhexyl 2-ethylhexylphosphonate and bis(2,4,4-trimethylpentyl)dithiophosphinic acid. Purified sulfuric acid 5 is obtained through the extraction step.

[0012] The acidic organophosphorus compound 4 may be diluted with a diluent, and the concentration of the acidic organophosphorus compound 4 may be adjusted as appropriate. Examples of the diluent include hydrocarbons such as kerosene and decane, and Class III petroleum products. A typical example of Class III petroleum products is MC531 manufactured by Tobu Chemical Co., Ltd. The concentration of the acidic organophosphorus compound 4 in the organic solvent consisting of the acidic organophosphorus compound and the diluent is preferably in the range of 10 to 40% by mass.

[0013] The sulfuric acid 1 may be concentrated sulfuric acid. The method for purifying sulfuric acid of the present invention may include an oxidation step (STEP 1 in Figure 1) in which the iron contained in the sulfuric acid 1 is oxidized by the oxidizing agent 2. The oxidizing agent 2 preferably contains at least one selected from the group consisting of hydrogen peroxide, potassium permanganate, and sodium hypochlorite, and more preferably at least one selected from the group consisting of hydrogen peroxide, potassium permanganate, and sodium hypochlorite.

[0014] The present invention's method for purifying sulfuric acid may include a dilution step (STEP 1 in Figure 1) in which the sulfuric acid 1 is diluted with water 3. The order of the oxidation step and the dilution step may be set as appropriate. The dilution step may be performed after the oxidation step, or the oxidation step may be performed after the dilution step, or the oxidation step and the dilution step may be performed simultaneously. Furthermore, the oxidation step and the dilution step may be performed multiple times in any order.

[0015] The present invention's method for purifying sulfuric acid may include a back-extraction step (STEP 3 in Figure 1) in which the extract obtained through the extraction step is back-extracted to obtain a back-extract 6 containing iron. The extract and an acid are mixed in the back-extraction step. The acid preferably comprises at least one selected from the group consisting of mineral acids, organic acids, and chelating acids, and more preferably at least one selected from the group consisting of mineral acids, organic acids, and chelating acids. The mineral acid preferably comprises at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, more preferably hydrochloric acid, and even more preferably hydrochloric acid. The organic acid is preferably oxalic acid, and more preferably oxalic acid. When oxalic acid is used, iron is back-extracted at a lower concentration than with mineral acid, so the amount of acid used can be reduced, which reduces costs and simplifies equipment design, making it highly practical for industrial use.

[0016] The sulfuric acid purification method of the present invention may include a reduction step in which a reducing agent is mixed with the purified sulfuric acid 5 and the purified sulfuric acid 5 is reduced. Although the redox potential of the sulfuric acid 1 increases in the oxidation step, the redox potential of the purified sulfuric acid 5 decreases in the reduction step. The reducing agent preferably contains at least one selected from the group consisting of oxalic acid, formic acid, and sulfite, and more preferably is at least one selected from the group consisting of oxalic acid, formic acid, and sulfite.

Examples

[0017] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

[0018] In the examples and comparative examples, the iron concentration was measured by an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0019] Example 1 50 L of 3M sulfuric acid and 50 L of 1M 2-ethylhexyl 2-ethylhexylphosphonate (PC-88A manufactured by Daihachi Chemical Industry Co., Ltd.) as an acidic organic extractant were mixed to extract iron in the sulfuric acid (extraction step). The obtained extract was back-extracted with 5 L of 0.5M oxalic acid (back-extraction step). Table 1 shows the iron concentrations in the aqueous phase before extraction and the aqueous phase after extraction in the extraction step, and the iron concentrations in the oil phase after back-extraction and the aqueous phase after back-extraction in the back-extraction step.

[0020] Example 2 The same operation as in Example 1 was carried out except that 1M bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex301 manufactured by Syensqo Co., Ltd.) was used as the acidic organic extractant. The results are shown in Table 1.

[0021] Example 3 The same operation as in Example 1 was carried out except that 5 L of 3M hydrochloric acid was used in the back-extraction step. The results are shown in Table 1.

[0022] Comparative Example 1 The same procedure as in Example 1 was followed, except that 1M (2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, manufactured by Syensqo Co., Ltd.) was used as the acidic organic extractant. The results are shown in Table 1.

[0023] [Table 1]

[0024] In Comparative Example 1, where the specified compound was not used as an acidic organic extractant, the iron extraction rate in the extraction step was low. On the other hand, in Examples 1 to 3, where the specified compound was used as an acidic organic extractant, the iron extraction rate in the extraction step was high. [Explanation of symbols]

[0025] 1. Sulfuric acid, 2. Oxidizing agent, 3. Water, 4. Acidic organophosphorus compound, 5. Purified sulfuric acid 6. Iron-containing back extract.

Claims

1. A method for purifying sulfuric acid, An extraction step of extracting iron from sulfuric acid using an acidic organophosphorus compound, and The extraction step includes a back extraction step in which the extract obtained through the extraction step is back-extracted with an acid to obtain a back extract containing iron. The acidic organophosphorus compound comprises at least one selected from the group consisting of 2-ethylhexyl 2-ethylhexylphosphonate and bis(2,4,4-trimethylpentyl)dithiophosphinic acid. The acid in question is oxalic acid, and the method is for purifying sulfuric acid.

2. A method for purifying sulfuric acid according to claim 1, further comprising a dilution step in which concentrated sulfuric acid is diluted with water.

3. A method for purifying sulfuric acid according to claim 1 or 2, further comprising an oxidation step in which iron contained in sulfuric acid is oxidized with an oxidizing agent.

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